Process for the preparation of phosphine



United States Patent 3,169,786 PRQCESS FOR THE PREPARATIGN 0F PHOSPI-il 3E George T. Miller, Lewiston, N.Y., and .iohn Steingnrt, St. Catharines, Qntario, anada, assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed July 27, 1960, Ser. No. 45,554 18 Claims. (Cl. 204-101) This invention relates to the preparation of phosphine by the reduction of phosphorus by electrolysis. More particularly this invention relates to the use of certain additives in the electrolyte of an electrolytic cell to improve the yield of phosphine produced therein.

Numerous processes have been developed for the preparation of phosphine. For example, phosphine has been prepared by the reaction of metallic phosphides or phosphonium halides with water, and by the hydrolysis of elemental phosphorus. These methods have been unsatisfactory because of the high production costs and/or because the phosphine product is in an impure form.

More recently processes and apparatus have been developed for the preparation of phosphine by electrolytic means. For example, in copending application SN 45,- 653, George T. Miller and John Steingart, filed of even date herewith, a method for the electrolytic production of phosphine is disclosed wherein an electrolytic cell having an anode and a solid cathode is employed, the lower portion of the cathode being in contact with a pool of molten phosphorus, whereby molten phosphorus forms a thin layer on the surface of the cathode above the pool of molten phosphorus. The cathode sections and anode sections of the cell also contain an electrolyte. When an electric current is passed between the cathode and anode through the electrolyte, a phosphine-containing gas is formed on the cathode and a gas such as oxygen is formed at the anode.

Another type of electrolytic cell for the production of phosphine is shown in copending application SN 45,654, George T. Miller and John Steingart, filed of even date herewith. The novel cell design shown in this application is comprised of a horizontal cathode positioned below a pool of molten phosphorus and above a horizontal anode; the cathode, molten phosphorus and anode being in contact with an electrolyte.

Phosphine has been produced in high yields and purity when employing the process and apparatus of the aforesaid copending applications. However, it has been observed that under certain conditions, with continued operation of the cell for extended periods, the yield of phosphine in the catholyte gas gradually diminishes.

It is an object of this invention to provide an improved method of preparing phosphine.

A further object of the invention is to provide novel additives for the electrolyte in the production of phosphine by electrolytic methods.

These and other objects of the invention will be apparent from the following detailed description. It has now been discovered that high yields of phosphine can be produced in the cathode section of electrolytic cells containing molten phosphorus in contact with the oath ode, when certain metallic ions are present in the electro-lyte.

In more detail, the improved results of this invention are obtained when ions of certain metals such as lead, tin, bismuth, antimony, cadmium, zinc, mercury, barium, calcium, silver, cobalt and mixtures thereof are present in the electrolyte of electrolytic cells employed in the preparation of phosphine.

Various methods may be employed for adding the ion to the electrolyte. For example, when a consumable anode such as a lead anode is employed, lead ions are transferred to the electrolyte and conveyed to the area adjacent to the cathode. If desired, the metal in finely divided form, may be added directly to the electrolyte, and dissolved therein. In another embodiment of the invention, salts and other compounds of the metals may be added to the electrolyte. For example, acetates of the metals such as lead acetate, chlorides of the metals such as barium chloride and zince chloride, phosphates of the metals such as cadmium phosphate and calcium phosphate may be employed. It is preferred to incorporate the metal ions in the electrolyte by adding a salt or other compound of the metal, but satisfactory results can be obtained by any of the above methods of adding the metal ion to the electrolyte.

Any effective concentration of metal ion-s in the electrolyte may be employed. For example, satisfactory results are obtained when the concentration of the metal ion is between about 0.03 percent and about 3 percent by weight of the electrolyte, but greater or lesser concentrations may be employed if desired.

The improvement of this invention is not limited by the design of the electrolytic cell. Typical examples of suitable designs of electrolytic cells are disclosed in the aforesaid copending applications, SN 45,653 and SN 45,654. The cell vessel is provided with an anode, a cathode and an electrolyte, A porous diaphragm is preferably employed to separate the cell into a cathode section and an anode section. Molten phosphorus is maintained in contact with the cathode. Suitable means are provided for recovering the phosphine-containing catholyte gas and, if desired, means may also be provided for recovering the anolyte gas.

Suitable anode materials include lead, lead-antimony alloys, lead dioxide, platinum, graphite, and stainless steel.

Any material having a hydrogen overvoltage as normally measured in the absence of phosphorus exceeding the hydrogen over-voltage of smooth platinum may be employed as the cathode. Typical cathodic materials include lead, lead-mercury amalgam, tin, mercury, cadmium, copper, bismuth, aluminum, zinc, brass, silver, nickel, gold and alloys thereof. For example, various tin-bismuth alloys, bismuth-lead alloys, lead-tin alloys, and nickel alloyed with such metals as iron, copper, chromium and the like may be employed. Black phosphorus may also be employed as a cathode material. The cathode may be positioned horizontally, vertically or otherwise in the cathode section. When a solid cathode is employed it may have the form of a helical coil, wire gauze or screen, perforated sheet, porous sponge metal, metal wool, plate and the like.

Suitable electrolytes include aqueous solutions of compounds such as phosphoric acid, sulfuric acid, hydrochloric acid, sodium chloride, lithium chloride, potassium chloride, sodium sulfate, potassium sulfate, monosodium phosphate, disodium phosphate, acetic acid, ammonium hydroxide and mixtures thereof. The concentration of the compound may vary between about 5 and about percent by weight, and is preferably between about 10 and about 50 percent by weight.

The cathodic current density necessary to give best results will vary with the cell design and the construction of the cathode. For example, current densities on the cathode between about 1 and about 200 amperes per square foot at a voltage between about 2 and about 25 volts give good results. However, any current density consistent with the economic production of phosphine may be employed.

While we do not Wish to be held to any theory it is believed that when an electric current is passed through the cell the metal ions contained in the electrolyte are aware-e reduced to metal at or near the cathode. The active metal apparently reacts with molten phosphorus to form the corresponding metal phosphide, which in turn is reduced by nascent hydrogen to phosphine and the metal. The reformed metal is then available to form additional metal phosphide in a cyclic manner. Thus continuous and high yields of phosphine are probably dependent on the stability of this cycle. If metal deposits on the cathode, or if the metal ions form a metal phosphied that is difficult to reduce, the cycle is broken or diminished and more metal ions are needed to replace those which have been lost. This concept is believed to be independent of the anode, except in such cases where a consumable anode is employed to supply metal ions to the electrolyte. V

The following examples are given to further illustrate the invention without any intent to be limited thereby.

Example 1 A cell was constructed as follows: into a two hundred cc. beaker was placed a solution of forty percent phosphoric acid. The beaker was heated to ninety degrees centigrade by external means. A rubber stopper having assembled therein the other cell elements, was then placed in the beaker. The assembly comprised a platinum anode contained in a porous ceramic tubular diaphragm and was adapted to vent oxygen gas from. the anode, a thermometer, and a lead cathode sheet one inch by three inches having a cathode lead wire and having a vent tube adapted to exit the phosphine and hydrogen gases from the cathode. When the assembly was placed in the beaker, the bottom edge of the cathode was adjusted to be immersed a a layer of molten phosphorus on the bottom of the beaker.

In starting up the cell, the current was turned on to make the cathode cathodic; this reduced oxides on the surface of the cathode. Next the cell was purged with nitrogen, and enough molten yellow phosphorus was added to cover the bottom of the cell, and to be in contact with the bottom edge of the vertical lead cathode.

Again the current was turned on, so that 0.5 ampere of electricity flowed at about 2.9 volts. The phosphorus began to Wick up both sides of the cathode to the top. Oxygen was produced at the anode, and phosphine began to be produced with hydrogen at the cathode. After an hour the surfaces of the cathode were totally covered with phosphorus. The temperature had increased to eighty-five degrees centigrade. The phosphine content of the cathode gas was determined by selective absorption in a solution of NaOBr. The cathode gas analysis gradually enriched in phosphine as more and more of the cathode surface was coated with phosphorus. The phosphine yield reached a maximum of seventeen percent after four hours.

Two grams of lead acetate in enough hot water to .dissolve the salt were added to the electrolyte. A large white precipitate, probably of lead phosphates, was formed. The phosphine yield increased to thirty-three percent in thirty minutes and in thirty more minutes had increased to forty percent phosphine.

Example 2 Using the cell and the electrolyte of Example 1, containing forty percent phosphoric acid and the lead salt, the platinum anode was changed to a lead anode. This caused the phosphine yield to increase to over eighty-five percent phosphine, after three hours operation. After running overnight, it still was yielding eighty-sevcn percent phosphine.

Example 5 In a cell of duplicate construction with that of Example 1, two grams of bismuth nitrate pentahydrate were added. The cell was operated at from 0.5 to l ampere at 3 to 3.5 volts at seventy-five degrees to eighty degrees'centigrade. After one day of operation the catholyte gas was ninety percent phosphine. This analysis decreased to vary between fifty-seven and seventy percent phosphine for a total of twenty-four days of operation.

Example 4 In a cell of duplicate construction with that of Example 1, one gram of cadmium acetate was added to the electrolyte. At seventy-five degrees centigrade, 0.5 ampere and 3.4 volts, a maximum or ninety-two percent phosphine was found in the cathode gas. After three days of operation, the cathode gas was found to containn bet-ween forty-eight and eighty-four percent phosphine.

Example 5 In a cell of duplicate construction With that of Example 1, two cubic centimeters of a saturated aqueous solution of mercuric nitrate were added. The current was slowly increased from 0.5 ampere at 4 volts to 1.9 amperes at 13.2 volts. The catholyte analysis increased from ten percent phosphine to seventy percent phosphine.

Example 6 A cell was made of duplicate construction with that of Example 1 except that a lead-bismuth alloy cathode and tin anode were used. The tin anode was retained in the cell for eleven hours, platinum being used otherwise. A cathode gas analysis of greater than ninety percent phosphine was obtained for six days at 0.5 ampere, 3.9

volts and seventy-four degrees centigrade. In seven more days of operation, the analysis had dropped to thirty percent phosphine. Reinsertion of the tin as anode for two hours resulted in the cathode gas analysis increasing to eighty percent phosphine.

Example 7 In a cell of duplicate construction with that of Example 1, an electrolyte of forty percent phosphoric acid was used. A cathode gas product was recovered analyzing 8.5 percent phc-sphine. The cell was operated at temperatures from seventy-one to seventy-four degrees centigrade, and at from between 3.5 and 3.9 volts with a current flow of from between 0.2 and 0.8 ampere. Then four cubic centimeters of ten percent barium chloride solution were added to the electrolyte. After one hour the cathode product yield had increased to fourteen percent phosphine, and after five more hours the yield had increased to twentythree percent phosphine. The cell was allowed to run overnight and after seventeen hours, the yield of phosphine was still twenty-one percent.

Example 9 Example 10 In a cell of duplicate construction with that of Example 1, an electrolyte of forty percent phosphoric acid was used. The cell was operated at eighty degrees centigrade, and 3.6 volts with 0.5 ampere of current and gave a cathode product yield of 5.5 percent phosphine. Four cubic centimeters of ten percent zinc chloride solution were added, and after an hour the cathode product yield had increased to eleven percent phosphine.

Example 11 In a cell of duplicate construction with that of Exampre 1, an electrolyte of forty percent phosphoric acid was used. The cell was operated at eighty degrees centigrade and 3.9 volts, with a current flow of 0.5 ampere to give a cathode product yield of 7.5 percent phosphine. Four cubic centimeters of ten percent calcium phosphate solution were added and after twenty-five hours the cathode product yield had increased to 25.9 percent phosphine.

Example 12 A cell of duplicate construction with that of Example 1 was employed, except that a one inch by three inch cathode of Mumetal (which is an alloy of 77.2 percent nickel, 4.8 percent copper, 1.5 percent chromium and 14.9 percent iron), and an electrolyte of forty percent phosphoric acid were used. The cell was operated at about ninety-five degrees centigrade, and 2.5 volts with 0.5 ampere of current. No phosphine was produced. Four cubic centimeters of ten percent lead acetate were then added and the phosphine yield increased to fifty-five percent phosphine in one hour. After 4.5 hours the cell was still yielding a cathode product of fifty-nine percent phosphine. The cell was run overnight and after sixteen more hours was producing a cathode product of eighty-five percent phosphine.

It Will be recognized by those skilled in the art that various modifications within the invention are possble, some of which have been referred to above. Therefore, we do not wish to be limited except as defined by the appended claims.

We claim:

1. A process for producing phosphine which comprises contacting an anode and a cathode with an aqueous electrolyte, contacting a portion of said cathode with molten phosphorus, passing an electric current between said anode and said cathode through said electrolyte while maintaining metallic ions in at least a portion of the liquid phase formed by said electrolyte and said molten phosphorus, and recovering the phosphine-containing gas produced at said cathode.

2. The process of claim 1 wherein said metallic ions are maintained in said electrolyte by employing a consumable anode.

3. The process of claim 1 wherein said metallic ions are maintained in said electrolyte by dissolving compounds of the metal in said electrolyte.

4. The process of claim 1 wherein said metallic ions are maintained in said electrolyte by dissolving finely divided metal in elemental form in said electrolyte.

5. The process of clam 1 wherein said metallic ions are ions of a metal selected from the group consisting of lead,

tin, bismuth, antimony, cadmium, zinc, mercury, barium, calcium, silver, cobalt and [mixtures thereof.

6. The process of claim 1 wherein said metallic ions are lead ions.

7. The process of claim 1 wherein said metallic ions are cadmium ions.

8. The process of claim 1 wherein said metallic ions are bismuth ions.

9. The process of claim 1 wherein said metallic ions are tin ions.

10. The process of claim 1 wherein said metallic ions are mercury ions.

11. The process of claim 1 wherein the concentration of metallic ions in said electrolyte is between about 0.03 percent and about three percent by weight.

12. A process for producing phosphine which comprises contactim an anode and a cathode with an aqueous phosphoric acid electrolyte, contacting a portion of said cathode with molten phosphorus, passing an electric current between said anode and said cathode through said electrolyte, while maintaining metallic ions in said electrolyte in a concentration of between about 0.08 percent and about three percent by weight of said electrolyte, and recovering the phosphine containing gas product at said cathode.

13. The process of claim 12 wherein said metallic ions are ions of a compound selected nErom the group consisting of lead, tin, bismuth, antimony, cadmium, zinc, mercury, barium, calcium, silver, cobalt and mixtures thereof.

14. The process of claim 12 wherein said metallic ions are lead ions.

15. The process of claim 12 wherein said metallic ions are cadmium ions.

16. The process of claim 12 wherein said metallic ions are bismuth ions.

17. The process of claim 12 wherein said metallic ions are tin ions. l

18. The process of claim 12 wherein said metallic ions are mercury ions.

References Cited in the file of this patent UNITED STATES PATENTS 1,375,819 Blumenberg Apr. 26, 1921 2,867,568 Cunningham Jan. 6, 1959 2,913,383 Topfer Nov. 17, 1959 FOREIGN PATENTS 1,130,548 France 'Oct. 1, 1956 OTHER REFERENCES Ephraim: Inorganic Chemistry, 5th edition, 1948, pages 6l7-622.

Pauling: College Chemistry, 1955, pages 330-335. Journal of Chemical Society, volume 16 (1863), pages 263-72. 

1. A PROCESS FOR PRODUCING PHOSPHINE WHICH COMPRISES CONTACTING AN ANODE AND A CATHODE WITH AN AQUEOUS ELECTROLYTE, CONTACTING A PORTION OF SAID CATHODE WITH MOLTEN PHOSPHORUS, PASSING AN ELECTRIC CURRENT BETWEEN SAID ANODE AND SAID CATHODE THROUGH SAID ELECTROLYTE WHILE MAINTAINING METALLIC IONS IN AT LEAST A PORTION OF THE LIQUID PHASE FORMED BY SAID ELECTROLYTE AND SAID MOLTEN PHOSPHORUS, AND RECOVERING THE PHOSPHINE-CONTAINING GAS PRODUCED AT SAID CATHODE. 